A variety of methods and processes are currently available to determine, identify and enumerate bacteria in different types of samples. For example, methodologies are available to identify and enumerate coliform bacteria, coliforms, in samples of water, food or dairy products in order to assess the quality or potential contamination levels of those samples.
One approach to distinguish E. coli, a specific type of coliform bacteria commonly classified as a Gram-negative rod bacteria, from a mixed population of coliforms is reported in U.S. Pat. No. 5,210,022. In that patent, two substrates which form contrasting insoluble precipitates in the presence of two specific bacterial enzymes, beta-galactosidase and beta-glucuronidase, are incorporated in a test medium. The use of these two substrates allows coliforms to be differentiated from E. coli because all coliform bacteria produce beta-galactosidase while only E. coli produce beta-glucuronidase. As the different colonies of bacteria grow when incubated in the substrate-containing medium, contrasting colored precipitates form around either growing E. coli or coliform colonies. Identification of E. coli colonies from the other coliform colonies in the mixed population is readily made by the contrasting colors of the precipitated substrates.
A need for such selective differentiation exists for other kinds of bacteria which are pathogenic or which are associated with harmful effects in humans, such as Salmonella, staphylococci, or Streptococcus. Efficient methodologies to identify and enumerate staphylococci, commonly classified as a Gram-positive coccus bacteria, in food samples are particularly needed because staphylococcus enterotoxin associated with staphylococci contamination of chicken, other processed meats and dairy products is the agent responsible for most common cases of food poisoning.
Processes and products which allow for the identification and/or enumeration of such bacteria would provide significant benefit to a variety of industries including, but not limited to, manufacturers of food products, cosmetics and diagnostic assays.